Large group of islands (11)
I believe the answer is:
archipelago
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">large group of islands</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for archipelago that I've seen before include "Cluster of islands" , "Bahrain, for one" , "watery domain" , "the Aegean, originally" , "Philippines, say" .)